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Earthing means setting up an electrical bond between a given point in a network, installation or machine and an earth electrode. This earth electrode is a conductive part which may be inserted in the ground or in a conductive medium, in electrical contact with the Earth.
Earthing thus involves using a wire conductor to connect an earth electrode to the metal chassis earths which might accidentally come into contact with the electric current due to an insulation fault on an electrical device. In this way, there will be no danger for people because the fault current will have drained into the earth.
There are several ways to ensure grounding of SSR assemblies:
-Solid State Relays have a protective earth connection ; or
-Their construction ensures a good connection to its fixing mean (Din rail, plate, panel,...) having themself a protective earth connection.
For the second case, a test can be performed according to EN60950-1 (2.6.3.3) :
“If the current rating of the circuit under test exceeds 16A, the test current and the duration of the test are as follows :
-two times the current rating of the circuit for 2min ; or
-as specified by the manufacturer for d.c. powered equipment ;
and the voltage drop across the PROTECTIVE BONDING CONDUCTOR shall not exceed 2,5V.”
EN60947-4-3 refers to EN60947-1 and does not require any test. This is why we recommend to test according to EN60950-1.
For panel mount SSR
If you mount the product on the panel, how do you connect the product grounding to the panel?
1) If our Solid State Relay is fixed on an isolated plate, the grounding must be done with a wire and a tab attached to one fixing screw.
This case is rare and this solution is not in compliance with EN60947-4-3.
2) If our SSR is fixed on a metal plate, the grounding of its plate is done by the fixing screws. The grounding of the assembly must be done with a wire, a tab and a bolt attached through a separate hole from fixing screws. If the plate is painted, the paint must be removed around the fixing screws and the protective earth connection.
This case is common and this solution is compliant with EN60947-4-3.
For Solid State Relays mounted on heatsink
Is there any grounding connection between the heatsink and the product ?
If our Solid State Relay is mounted on a heatsink, the grounding of its plate is done by the fixing screws. The grounding can be done with different ways:
-The heatsink has a protective earth connection : this is OK.
As an option, a test can be performed according EN60950-1 (2.6.3.3)
This solution is in compliance with EN60947-4-3.
-The heatsink has no protective earth connection and assembly is fixed on a DIN rail or a metal panel which has a protective earth terminal : this is OK.
A test can be performed according EN60950-1 (2.6.3.3)
This solution is compliant with EN60947-4-3.
-The heatsink has no protective earth connection and assembly is fixed on an isolated plate : the grounding must be done with a wire and a tab attached to one fixing screw.
This case is rare and this solution is not in compliance with EN60947-4-3.
Usually, the heatsinks have several possibilities for grounding connection. Here are some examples :
For Din-Rail mount Solid State Relays :
If you use the DIN rail as grounding mean, the SSR assembly will fulfill the EN60950-1 (2.6.3.3) removing the need of a protective earth connection on the Solid State Relay.